The invention is based on an electrical insulator. Such an insulator is used in medium-voltage and high-voltage engineering as a mechanically and thermally highly-loaded part such as, for example, a pressure-stressed arcing chamber housing of compressed-gas circuit breakers or a compartmental insulator in gas-insulated metal-encased switching stations. Since filler-reinforced thermosets having glass transition temperatures of up to approximately 120.degree. C. are used as material for said insulator, such an insulator can be exposed to temperatures of not more than 85.degree. C. if highly stressed mechanically during continuous operation. Although thermosets with higher glass transition temperatures are known, these materials are very brittle and are therefore not suitable for use in a mechanically-stressed electrical insulator.